Some NOS tubes may have a lower voltage rating. Take 6SN7 as an example. The NOS 6SN7GT has a max plate voltage of 300V. The newer 6SN7GTA/B have a higher voltage at 450V.
Damsel in Distress with Jadis DPL
Caught the tube rolling bug and acquired a pair of 12AU7 "supposedly" NOS Phillip Mullard collaboration tube along with a RCA 12AX7 for my Jadis DPL preamp. Experienced a loud crack from left channel through my loud speaker. Left speaker went completely dead. Removed all 3 tubes and re-installed original compliment. Everything is back to normal. Or so it seems. What happened? Did I do any damage? Any comments welcome ~ Deb